Learn English – What’s the shape of the upper half of a sphere called

I don't see a "circular" bit at the top of the arch in the OP's picture.

The parts of the arch are:

• The absolute top of the arch is the apex.
• The curve at the top of the arch is known as the crown.
• The point at which the curve begins is the springing or spring-line.
• The curve between the springing and the crown is known as the haunch.
• The inner curve of the arch is the intrados.
• The outer curve is the extrados.
• The arch itself is made of sections called voussoirs. So the crown and the haunch are made of a number of voussoirs.

Most people would call that sort of thing wrinkled or maybe pruned, perhaps even corrugated if they were particularly prone to long words.

Wikipedia writes:

The wrinkles that occur in skin after prolonged exposure to water are sometimes referred to as pruney fingers or water aging. This is a temporary skin condition where the skin on the palms of the hand or feet becomes wrinkly. This wrinkling response may have imparted an evolutionary benefit by providing improved traction in wet conditions, and a better grasp of wet objects.